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可恶的NetCore对DataTable支持的不好，这对于喜欢直接写SQL的童鞋来说非常难受，因此，在NetCore项目中有必要引入优秀的第三方数据库中间件，目前市场上比较优秀的第三方EF框架有很多，例如： Sqlsugar 、 Dapper 、 FreeSql 等，当然，微软也有自己的一套EF框架，EntityFrm 和 EfCore，就效率而言，第三方的框架要完胜微软的EF框架，真不知道微软是干啥吃的、

今天，我们使用Dapper这个轻量级的第三方EF框架。

1.安装Dapper

这里直接使用Nuget安装。

安装完成后，我们需要对Dapper进行扩展，如下：

using Microsoft.Extensions.Configuration;
using System;
using System.Data;
using System.Data.SqlClient;
using WuAnCommon;
namespace WuAnSqlService
    public class DapperHelper
        /// 获取连接字符串        
        private static string Connection= ConfigCommon.Get("WuAnDBContext");
        /// 返回连接实例        
        private static IDbConnection dbConnection = null;
        /// 静态变量保存类的实例        
        private static DapperHelper uniqueInstance;
        /// 定义一个标识确保线程同步        
        private static readonly object locker = new object();
        /// <summary>
        /// 私有构造方法，使外界不能创建该类的实例，以便实现单例模式
        /// </summary>
        private DapperHelper()
            // 这里为了方便演示直接写的字符串，实例项目中可以将连接字符串放在配置文件中，再进行读取。
        /// <summary>
        /// 获取实例，这里为单例模式，保证只存在一个实例
        /// </summary>
        /// <returns></returns>
        public static DapperHelper GetInstance()
            // 双重锁定实现单例模式，在外层加个判空条件主要是为了减少加锁、释放锁的不必要的损耗
            if (uniqueInstance == null)
                lock (locker)
                    if (uniqueInstance == null)
                        uniqueInstance = new DapperHelper();
            return uniqueInstance;
        /// <summary>
        /// 创建数据库连接对象并打开链接
        /// </summary>
        /// <returns></returns>
        public static IDbConnection OpenCurrentDbConnection()
            if (dbConnection == null)
                dbConnection = new SqlConnection(Connection);
            //判断连接状态
            if (dbConnection.State == ConnectionState.Closed)
                dbConnection.Open();
            return dbConnection;
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上述代码完成Dapper对数据库的连接，下面还需要Dapper操作数据库的公共类，如下：
    public static class DapperDbContext
        // 获取开启数据库的连接
        private static IDbConnection Db
                //创建单一实例
                DapperHelper.GetInstance();
                return DapperHelper.OpenCurrentDbConnection();
        /// <summary>
        /// 查出一条记录的实体
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static T QueryFirstOrDefault<T>(string sql, object param = null)
            return Db.QueryFirstOrDefault<T>(sql, param);
        public static Task<T> QueryFirstOrDefaultAsync<T>(string sql, object param = null)
            return Db.QueryFirstOrDefaultAsync<T>(sql, param);
        /// <summary>
        /// 查出多条记录的实体泛型集合
        /// </summary>
        /// <typeparam name="T">泛型T</typeparam>
        /// <returns></returns>
        public static IEnumerable<T> Query<T>(string sql, object param = null, IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null)
            return Db.Query<T>(sql, param, transaction, buffered, commandTimeout, commandType);
        public static Task<IEnumerable<T>> QueryAsync<T>(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
            return Db.QueryAsync<T>(sql, param, transaction, commandTimeout, commandType);
        public static int Execute(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
            return Db.Execute(sql, param, transaction, commandTimeout, commandType);
        public static Task<int> ExecuteAsync(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
            return Db.ExecuteAsync(sql, param, transaction, commandTimeout, commandType);
        public static T ExecuteScalar<T>(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
            return Db.ExecuteScalar<T>(sql, param, transaction, commandTimeout, commandType);
        public static Task<T> ExecuteScalarAsync<T>(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
            return Db.ExecuteScalarAsync<T>(sql, param, transaction, commandTimeout, commandType);
        /// <summary>
        /// 同时查询多张表数据（高级查询）
        /// "select *from K_City;select *from K_Area";
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static SqlMapper.GridReader QueryMultiple(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
            return Db.QueryMultiple(sql, param, transaction, commandTimeout, commandType);
        public static Task<SqlMapper.GridReader> QueryMultipleAsync(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
            return Db.QueryMultipleAsync(sql, param, transaction, commandTimeout, commandType);
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有了上述代码，我们就可以写数据库方法了
示例代码：
        public BaseResponse<List<WuAnTestModel>> GetDataDapper()
               return CommonBaseResponse.SetResponse<List<WuAnTestModel>>(DapperDbContext.Query<WuAnTestModel>("select DeviceNo,DeviceSecret from Yk_Device").ToList(),true);
            catch (Exception ex)
                throw ExceptionHelper.GetAggregateException("WuAnService.WuAnTestService", "GetDataDapper", "", ex);
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当然，我这个扩展类比较简单，如果需要更复杂的扩展类，可以进行百度，毕竟大家都是面向百度编程。
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